The present invention relates to a servo press system that includes a servo press that moves a slide upward and downward by rotating a crank shaft, and a servo transfer device that transfers a workpiece to the servo press.
A press machine may typically be classified as a press that includes a motor and a flywheel that are rotated at a constant rotational speed, or a servo press that moves a slide upward and downward by controlling the rotation of a servomotor. These presses significantly differ in slide motion.
The former is configured so that the rotational speed of the crank shaft is constant (see (B) in FIG. 6), and the slide motion via the crank mechanism is also constant (see (A) in FIG. 6).
The latter is configured so that the slide motion can be set arbitrarily. Specifically, the slide can be displaced at low speed within one cycle, and can be stopped at a given position. It is also possible to cause the crank shaft to make a reciprocating rotation motion (pendulum motion) within an arbitrary angular range. It is obvious from the following comparison that the latter is superior from the viewpoint of diversity of the press operation and an improvement in productivity.
The press operation that utilizes the pendulum motion is implemented by causing the crank shaft to make a reciprocating motion at a rotation angle of 60°, 180°, and 300°, for example (see (A) in FIG. 7). The rotational speed of the crank shaft is illustrated in (B) in FIG. 7. The slide reaches the upper limit position when the rotation angle is 60° or 300°. The upper limit position is lower than the position (top dead center position) when the rotation angle is 0° or 360°. Specifically, since an unnecessary rotational motion (rotation time))(300°-360°-60°) can be omitted, the number of press operations at a rotation angle of 180° (bottom dead center position) can be increased (i.e., the cycle time can be reduced).
It is important to solve practical problems that occur during the operation so that the servo press comes into widespread use. For example, it is difficult to determine the relative relationship between the slide position and the rotation angle of the crank shaft of the servo press. For example, the slide is set at the upper limit position (top dead center position) when the rotation angle is 0°(360°) (see (A) in FIG. 6). However, the servo press is configured so that the slide is set at the upper limit position when the rotation angle is 60° or 300° (see (A) in FIG. 7), and the upper limit position (value) differs from (is lower than) the top dead center position (value) (see (A) in FIG. 6). The servo press is also configured so that the rotation angle is not set at 0° (360°) during the press operation. Moreover, the slide position may be identical at different rotation angles. It is difficult to intuitively understand these issues.
Therefore, the slide motion setting operation, the operation of setting the generation timing of a timing signal or a synchronization signal corresponding to the slide motion, and the die height adjustment operation become troublesome, and the working efficiency decreases. The servo press is more troublesome for a person who is accustomed to another press (e.g., a press having a vertical slide drive mechanism), and an erroneous operation may easily occur.
An improvement that utilizes a virtual rotation angle has been proposed (see JP-A-11-245097 and JP-A-2004-58152, for example). In JP-A-11-245097, one stroke of the slide motion is converted into 360°, and the bottom dead center is set corresponding to a rotation angle of 180°. The timing setting and the like can be changed on the motion curve displayed using the virtual rotation angle. In JP-A-2004-58152, the slide position is converted into a virtual crank angle, and displayed. The virtual rotation angle corresponding to the detected slide position is output to an external device.
It is necessary to increase the press speed in order to further improve the productivity. It is also necessary to reliably prevent interference. Since interference occurs based on the relative positional relationship between the press element (part) and the transfer device-side element (part) during the press operation, it is important to operate the press and the transfer device in synchronization.
When a servo press system utilizes an individual control method, the press and the transfer device are controlled independently. Therefore, it may be difficult to increase the operation speed, and prevent interference. When using a master-slave control method, a signal detected by the press is input to the transfer device so that the transfer device operates in synchronization with the press. When using an integrated control method, the press and the transfer device are operated in synchronization based on an identical signal. Each method is used arbitrarily, and is normally selected based on whether the productivity or prevention of interference is regarded as important.
It is effective to increase the operation speed by utilizing the pendulum motion from the viewpoint of an improvement in productivity, irrespective of the control method. In order to prevent interference, it is desirable to drive the transfer device taking account of the relationship with the actual behavior of the press-side part during operation.
The synchronization signal detection method, the synchronization signal detection position, the detector installation position, the signal generation circuit system, and the like may be implemented in various ways. The structure, the rigidity, the inertia, and the like of the transfer device may differ over a wide range. Therefore, an unexpected state may occur during the actual operation of a servo press system. For example, the synchronized operation of the servo press and the transfer device may temporarily become unstable (i.e., the operation of the servo press may be terminated), or deformation or breakage of the device may occur.